Media Channels and advertisers, are measuring the size of their audiences, so as to assess profitability of airtime. These measurements indicate the number of people that are exposed to the media content.
U.S. Pat. No. 8,358,966 B2 User exposure to media items is detected and measured. A mobile client device carried by a user digitally samples the audio environment of the user on a regular basis. These samples are transformed into a stream of data signatures and compared with reference media items to detect user exposure to the reference items. Purchase behavior following exposure to selected media content items can be detected and tracked as well, so as to gauge effectiveness of media items such as advertisements.